This chapter introduces approaches to materiality and biology within anthropological scholarship on sex and gender. It emphasizes how biological subfield of eco-evo-devo (which emerged in dialogue with feminist studies) can contribute to anthropological debates. The authors focus on hormones, signaling molecules that regulate many physiological processes in humans, animals, and plants. Hormones are a particularly productive site for considering how anthropologists interested in sex, gender, and bodies might benefit from additional attention to biological processes and biological knowledges, as they challenge prevailing concepts and categorical oppositions of self/world, nature/culture, and mind/matter. The authors first sketch out a history of the relationship between anthropology and biology and, within that history, how feminists have confronted biologism. They then introduce eco-evo-devo and explore how its insights about hormones and development can serve as a prompt to rethink the body within anthropology. Last, they review examples of social scientific engagement with hormones, arguing that a deeper engagement with the materiality of hormones rather than only with their popular representation can help anthropologists continue their ongoing efforts to reframe the social and apprehend gender and sexuality as entangled within complex ecologies of industrial capitalism.